New methods for treating insulin-dependant diabetes mellitus are presently being sought. At the present time, diabetes patients test their blood sugar levels and inject insulin when necessary. Although it is possible to transplant a pancreas from one human to another, the survival rate for this procedure is only 40% at one year following surgery. Researchers have used isolated pancreatic islets in transplantation approaches in attempts to find a viable long term treatment of diabetes.
The islets of Langerhans are clusters of differentiated cells sharing a common precursor. Found in the pancreas of mammals, islets taken together can be considered as a single endocrine organ. The islets occupy about 7% of the human pancreas which also contains the exocrine acinar tissue. The composition of cells in the islets differs depending on the location of the islet in the pancreas. Central to each islet is a core of insulin secreting beta cells. Surrounding the beta cells are somatostatin secreting delta cells, glucagon secreting alpha cells and pancreatic polypeptide containing f cells. Alpha cells tend to be concentrated in the tail and the body of the pancreas whereas, the f cells are concentrated in the head. This distribution corresponds to the embryonic origin of alpha and f cells from dorsal and ventral primordium of the pancreas.
Pancreatic beta cells are the only cells in which the insulin gene is expressed and, therefore, are the sole source of metabolic insulin in vertebrates. Insulin is necessary in maintaining glucose homeostasis and plays a role in the normal processing of proteins and fats. Insulin release can be inhibited by low levels of somatostatin and stimulated by glucagon. Without sufficient insulin to metabolize glucose, hyperglycemia occurs. Insulin-dependant diabetes mellitus is a direct result of nonfunctional islets, specifically beta cells.
Among the major obstacles in islet transplantation research is an inability to induce proliferation and to keep islets viable over time. Researchers have encountered many obstacles in attempting to cure diabetes resulting from the loss of islet function. For transplantation, it is necessary to preserve islet viability as well as gene expression and secretory function.
Pancreatic islets do not grow readily in primary cultures. However, these endocrine cells have been grown with difficulty as monolayers. This difficulty of long-term culture has not only hindered the laboratory research for such islets, but it has also hindered attempts to carry out physiological and even clinical studies with such islets. Therefore, there is needed a medium for the long-term proliferation of islets. A medium for the long-term survival of cells is additionally needed for other cell types.
Additionally, current methods of transplantation must suppress immune response by the host organism that may lead to rejection of the transplanted cells and loss of islet function. Thus, there is also a need in the art for a simple, non-invasive method of introducing hormone secreting cellular moieties, such as insulin secreting pancreatic islets, into a hormone deficient organism without requiring general immunosuppressive agents.